The requirements for the signal quality of transmitting devices become more stringent as the need for high data rates and increasing mobility grows. The modern mobile radio standards, such as Universal Mobile Telecommunications System (UMTS), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile Communication (GSM), Enhanced Data Rates for GSM Evolution (EDGE), Bluetooth Medium Data Rate or Wireless Local Area Network (WLAN) according to 802.11a/b/g require special modulation types for data transmission which modulate both the phase and the amplitude of a carrier signal at the same time.
Simultaneous amplitude and phase modulation makes it possible to achieve higher data transmission rates and thus better bandwidth efficiency. The mobile radio standards mentioned above envisage, for example, the use of quadrature phase shift keying (QPSK), eight phase shift keying (8-PSK), or quadrature amplitude modulation (QAM) as modulation types for the data transmission. Depending on the selected application for the individual mobile radio standards, these high-quality modulation types are used not only for data transmission from a base station to a mobile communication appliance but also from the mobile communication appliance to the base station.
Many modern mobile radio standards, as for example UMTS or GSM/EDGE, control the output power of a transmitted radio frequency signal. To this end, a gain factor of a power amplifier in a transmitter path can be set according to a desired output power. As the output power corresponds to an amplitude of the radio frequency signal, it is possible to derive a desired gain factor as a function of an actual amplitude value of the radio frequency signal and a reference amplitude value corresponding to the desired gain factor.
The actual amplitude value can be measured or detected using an amplitude detection circuit. FIG. 11 shows an embodiment of a conventional detection circuit which derives a detection signal as a function of a radio frequency signal at its input DIN. The detection circuit comprises a diode element D1. An anode terminal of the diode element D1 is coupled to the detector input DIN and to a voltage source V1 via a resistor R1. A cathode terminal of the diode element D1 is coupled to the detector output D0 and further to a reference potential tap VSS via a capacitor CS and a parallel connected resistor RD.
The voltage source V1 provides a bias voltage to the anode terminal of the diode D1. A radio frequency signal is received at the detector input DIN which adds to the bias voltage. During the positive alternation of the radio frequency signal a current through the diode D1 charges the capacitor CS up to a potential resulting from the bias voltage plus the amplitude of the radio frequency signal. During the negative alternation, the diode D1 is blocked, whereas the voltage at the detector output D0 remains mainly constant. A voltage difference between the anode and the cathode terminal of the diode D1, which is reversed biased during the negative alternation, results to almost two times the amplitude of the radio frequency signal.
Assuming that the voltage source V1 provides a bias voltage of 3V, the amplitude of the radio frequency signal equals to 5V and a voltage drop of the forward biased diode D1 equals to 0.5V, the capacitor CS will be charged up to a voltage of 5V+3V−0.5V=7.5V during the positive half-wave or alternation. During the negative half-wave or alternation, the voltage at the anode terminal of the diode D1 would result to 3V−5V=−2V, leading to a voltage difference of 7.5V−2V)=9.5V, which is almost twice the amplitude of the radio frequency signal of 5V.
It is therefore desired to dimension the diode D1 such that it withstands twice the expected maximum amplitude of the radio frequency signal.
The dynamic range of a detection circuit can be determined by a lower and an upper limit. The lower limit corresponding to a minimum amplitude to be detected can be defined as a minimum slope of a characteristic curve of the detection circuit, wherein the slope is defined as a ratio between an output voltage difference ΔUDET and an input amplitude voltage difference ΔURF. The upper limit of the dynamic range can be defined by the maximum amplitude to be detected without harming or destroying the detection circuit, especially the diode D1 because of extensive reverse biasing. In other words, the upper limit of the dynamic range can be a function of the breakdown voltage of the diode D1.
Modern mobile radio standards can require a wide dynamic range for the amplified radio frequency signal. To achieve a wider dynamic range, for example the withstand voltage of the detection circuit can be increased by changing technology parameters. However, this may affect the performance of the detection circuit. The dynamic range can further be enlarged by providing amplification or attenuation elements at the input of the detection circuit which both affects the characteristic curve of the detection circuit and conditions additional control circuits to control the amplification or attenuation elements.